The invention relates to an RF circuit arrangement comprising a travelling wave amplifier. The travelling wave amplifier comprises a succession of n amplifying devices, where n.gtoreq.2, each having an input and an output, a first successiong of inductances connected in series with one another, and a second succession of inductances connected in series with one another. A respective input capacitance is associated with the input of each of the amplifying devices and a respective output capacitance is associated with the output of each of the amplifying devices. The inputs of the amplifying devices are coupled to the first succession of inductances at junctions thereof and the outputs of the amplifying devices are coupled to the second succession of inductances at junctions thereof. The travelling wave amplifier has an input transmission line comprising the first succession of inductances and the input capacitances associated with the amplifying devices and having two ends, and has an output transmission line comprising the second succession of inductances and the output capacitances associated with the amplifying devices and having two ends.
At each frequency in the operating frequency range of the amplifier, for each pair of successive amplifying devices, the phase delays for electromagnetic energy propagating respectively along the input transmission line and along the output transmission line, between the coupling to the inputs and the outputs respectively of the pair of successive amplifying devices, are substantially equal. The capacitance associated with capacitance of the amplifying device itself and/or a separate capacitor which may be of a lumped or distributed form.
The concept of a travelling wave (or distributed) amplifier to provide amplification of RF signals over a broad frequency range was originally proposed many years ago in GB No. 460 562; the amplifying devices of the original proposal wre vacuum tubes. In recent years, there has been a considerable revival of interest in the proposal in order to provide amplification of microwave signals over a broad frequency range (for example as broad as 2-20 GHz) using Field Effect Transistors as the amplifying devices (see, for example, "Solid-State, Broadband Power Amplifiers for Electronic Warfare Applications" by T. A. Midford, Microwave Journal, February 1985, pages 95-116, and the references therein); this offers the possibility of integrating at least the travelling wave amplifier, and possibly a larger RF circuit arrangement comprising the amplifier, on a single substrate of semiconductor material.